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- Liu, Jinrong, 1995-
(författare)
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Lignin nanoparticles for photonic crystals and photothermal films
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of sustainable materials from biobased resources is essential due to environmental concerns posed by fossil-based materials. Lignin is a chemically complex biopolymer that exists in woody tissues of vascular plants. Lignin has many useful properties such as antioxidant activity, thermal stability, UV-absorbance, rigidity and so on. However, an inherent challenge of lignin relates to its complex molecular structures and poor solubility in water and common solvents. One strategy to utilize lignin is to fabricate lignin nanoparticles (LNP) that produce colloidally stable dispersions in water. This thesis aims to develop LNP-based materials which can be used in photonic crystals and photothermal films towards energy-efficient functional materials.The first part of the thesis focused on elucidation of the phenomena occurring during centrifugation-assisted assembly of LNP-photonic crystal (L-PC). L-PC with rainbow coloration or separate colors were produced by controlling the polydispersity index (PDI), particle size (150 to 240 nm), and assembly of LNPs. In a follow-up work, an improved method was developed to increase the yield of L-PCs. The effects of factors such as initial lignin concentration, and dilution time on the particle size and PDI of formed LNPs were studied. Empirical models were established to predict the size of LNPs and successfully used to control the resulting color of L-PCs. Moreover, the nanostructure of L-PCs was investigated. To harness lignin’s ability to absorb solar energy (light wavelength: 250–2500 nm), LNP-based composite films and coatings with photothermal performance were developed in the second part of the thesis. LNP-chitosan films and coatings were prepared and applied to indoor heat management. The LNPs content was adjusted from 10 to 40 wt%. By incorporating LNPs, the mechanical strength and photothermal properties of the films were improved compared to the pure chitosan film. Moreover, LNP-silver-chitosan (CC-Ag@LNP) films were prepared by using LNPs as a reducing agent. Silver ions were reduced on the surface of LNPs with UV-light assistance, and the hybrid nanoparticles were used to prepare films by casting. The CC-Ag@LNP films exhibited improved wet-strength and exhibited antibacterial performance against Escherichia coli (sterilization effect > 99.9%).Overall, this thesis contributes to both the fundamental insight in lignin aggregation to colloidal particles and showcases ways to control their assembly and incorporation into macroscopic materials with added functionality.
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| 2. |
- Morsali, Mohammad, 1992-
(författare)
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Site-specific reactions of softwood kraft lignin for biobased vitrimers and reactive colloidal particles
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignin, a natural polyphenolic compound of wood, holds promise as a green alternative to fossil resources given the current environmental concerns. However, its complex structure and limited usability have impeded widespread use of lignin in biobased materials. This thesis is focused on employing a series of chemistries and techniques that facilitate lignin utilization in a variety of applications ranging from bulk materials to colloidal particles. Lignin-based vitrimers, developed by a one pot, catalyst-free click addition of poly(ethylene glycol) divinyl ether to softwood kraft lignin and formation of dynamic acetal exchange network showed excellent performance as recoverable adhesives, reaching lab shear strengths of 2.6 MPa and 6.0 MPa for wood and aluminum substrates, respectively. Stabilized lignin nanoparticles synthesized by hydrothermal crosslinking of hydroxymethylated lignin nanoparticles showed an excellent colloidal stability in organic solvents such as ethanol, acetone, dimethylformamide, and tetrahydrofuran, and aqueous media (3 < pH < 12). These stabilized lignin nanoparticles were subjected to direct surface modification in colloidal state to develop aminated pH-responsive particles. Stabilized lignin nanoparticles, preserving redox activity, showed a capacity in reducing silver ions, forming hybrid lignin-silver nanoparticles for applications such as hydrogen peroxide colloidal sensors. Interaction of silver ions and stabilized lignin nanoparticles contributed to the emergence of discrete patterns of silver in lignin nanoparticle embedded hydrogels. The location and distance of the discrete patterns can be modified by altering the particle size and concentration. Furthermore, redox activity of stabilized lignin nanoparticles, hydroxymethylated lignin nanoparticles and unmodified lignin nanoparticles with different particle sizes (90 nm, 150 nm, 640 nm) were studied in charge storage applications in organic poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. Non-modified lignin nanoparticles with the diameter of 150 nm showed the best performance overall, with specific capacities of the electrode reaching 42.5 mAh/g at a current density of 1 A/g. These particles were also demonstrated in a Zinc-lignin battery prototype. To further explore and broaden the horizon of lignin applications, propargylated lignin nanoparticles demonstrated light-induced “click” reactions initiated thermally or by Cu (I) or energy-efficient light emitting diodes with 405 nm wavelength. These nanoparticles were further employed to demonstrate the light-triggered reactions with betulin azide in Pickering emulsions, showcasing the versatility of colloidal chemistry of lignin and opportunities for new applications.
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| 3. |
- Ribca, Iuliana, 1993-
(författare)
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Lignin-Based Thermosets with Tunable Mechanical and Morphological Properties : A Study of Structure-Property Relationships
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, there is an urgent need to decrease our dependence on fossilresources and shift towards the use of renewable resources for advancingsustainable development. Utilizing renewable and bio-based raw materials,such as lignocellulosic biomass, for designing new materials is a promisingapproach to promote this objective. The main components of lignocellulosicbiomass are cellulose, hemicellulose, and lignin. Lignin is the most abundantaromatic biopolymer in nature and it is produced on a large scale fromchemical pulping processes as technical lignin. Lignin has the potential as asustainable and renewable alternative to fossil-based aromatics in variousapplications, e.g. thermosetting resins.Technical lignin has a complex and heterogeneous structure, with arelatively low chemical reactivity. It is characterized by a high dispersity, thepresence of various functional groups that are unevenly distributed along thelignin chains, and various interunit linkages between the monoaromatics. Toovercome the challenges associated with lignin heterogeneity, technicallignin can be fractionated and/or chemically modified.In this work, LignoBoost Kraft lignin was used as a starting material toproduce lignin-based thiol-ene thermosets. Firstly, lignin was fractionatedusing two approaches: 1) sequential solvent fractionation, and 2) microwaveassistedextraction. These fractionation approaches enabled access to ligninfractions with unique and tunable properties. Subsequently, lignin waschemically modified, in particular through allylation. Two allylation reagentswere used: allyl chloride and diallyl carbonate. The use of allyl chlorideenables a selective allylation of the phenolic OH groups, leaving the aliphaticand carboxylic acid OH groups unmodified. On the other hand, diallylcarbonate can react with all the aforementioned OH groups, leading to ahigher degree of allylation. Subsequently, allylated lignin was thermallycross-linked with various polyfunctional thiols, leading to thiol-enethermosets. The structure-property relationships of the thermosets wereinvestigated by varying several parameters, including the lignin source,fractionation approach, chemical modification, and thiol cross-linker. Byadjusting these parameters, various thermosets with tunable mechanical andmorphological properties were produced. Understanding the structurepropertyrelationships of these bio-based materials is crucial for identifyingpotential applications.
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